1. Field
This application generally relates to the field of wireless communication systems, and more particularly to signals and protocols that enhance data transmission efficiency in such systems.
2. Related Art
The subject matter set forth herein is applicable to wireless communication systems that multiplex signals using techniques of time division multiplexing (TDM), code division multiplexing (CDM), and frequency division multiplexing (FDM). However, it has been developed primarily in the context of CDMA (Code Division Multiple Access) cellular telecommunication systems that provide high-speed connectivity including data and voice transport on both point-to-point and point-to-multipoint bases. First-generation (analog) and second-generation (digital) cellular networks were used primarily for communicating voice traffic via mobile cellular telephones, and thus maintained a focus on access methods for the efficient transport of voice information. With the rising popularity of the Internet, a third-generation (3G) wideband multimedia cellular network continues to be developed to transport both voice and data at much higher speeds than were previously available using the first and second generation wireless networks.
A Third Generation Partnership Project 2 (3GPP2) has been established by industry groups for the purpose of defining specifications to transition current code-division multiple-access (CDMA) wireless networks to the third generation, which is commonly referred to as CDMA2000. One such specification may be referred to as “IS-856,” also called (CDMA system) “EV-DO.” Rev 0 and Rev A IS-856 specifications have been published and are available from the 3GPP2 organization as IS-856 and IS-856-A (also C.S0024-A, C.S0024-B), and are incorporated by reference herein in their entireties for teachings on communications protocols used in 3G wireless communications systems.
The 3GPP2 organization is primarily concerned with defining specifications for CDMA systems such as are implemented in North America. A document specifying a somewhat different CDMA system, such as is used more commonly in Europe, may be identified as 3GPP TSG-RAN Release-5, and is hereby incorporated by reference for its teachings on CDMA systems.
Cellular communications systems traditionally provided almost exclusively telephone voice connectivity, with data transfer only in support of the voice connection or as possible with audio-frequency modems. The systems are evolving toward an ability to convey high rate packet data “HRPD” between base stations (“BSs”) or “Access Networks” (“ANs”) to mobile stations (“MSs”) or “Access Terminals” (“ATs”).
European countries have previously employed GSM technology for telephone operation, which is based on time division multiplexing (“TDM”). As the European systems are modified to accommodate high rate packet data, CDMA is being adopted as a new technology. Being new, no provision need be made for MSs or BSs configured to operate in accordance with earlier generation or “legacy” CDMA standards. These countries are adopting a wideband version of CDMA, WCDMA, which employs a 5 MHz physical communication channel that is four times as large as the 1.25 MHz bandwidth of carriers in existing CDMA systems, such as are widely deployed in the United States.
In countries such as the United States that have a large installed base of CDMA systems, it will be useful to increase high speed data communication capacity while remaining compatible with legacy devices and architectures. This issue has been addressed in many papers submitted to the 3GGP2 organization, such as C30-20050314-044R1_QCOM_MultiCarrier_HRPD_PhysicalLayer.pdf.
Packet data communications typically rely on transmitting packets at the minimal power that is statistically likely to cause correct reception. The power of signals transmitted to other receivers appears as general “noise” to a particular receiver (e.g., an MS) to which the signals are not directed, reducing their ability to correctly receive their own signals. Thus, minimizing power is well understood to leave system capacity to serve more receivers, which is very desirable. Employing minimum power for a particular packet necessarily entails a statistical probability of transmitting unsuccessfully. Unsuccessfully transmitted packets must be retransmitted, or otherwise clarified, to ensure that the data is ultimately received correctly. Consequently, Automatic Retransmission reQuest (ARQ) techniques are employed that rely on reverse link acknowledgment signaling to enhance data transfer efficiency.
Higher rates of data transfer are made possible by various techniques, typically including increasing data density through more complex modulation schemes and more efficient (but less redundant) coding techniques. The techniques that increase data rate generally decrease the accuracy of reception. MSs that are receiving data are in the best position to determine whether the received signal is good enough to successfully support a higher data rate, or whether a lower data rate should be used to improve reception accuracy. MSs therefore are typically designed to provide Data Rate Control instructions to the serving station, in order to constantly adjust for the best tradeoff between speed and accuracy.
Unlike basic voice transmission requirements, packet data transmission is often asymmetric between a forward link (FL) and a reverse link (RL), as a data file, for example, is transferred on the FL direction without corresponding data transmission on the RL. Indeed, the designation as FL and RL may be taken to reflect a direction of primary data transfer, and need not refer to transmissions from a serving base station and from a terminal station, respectively. Typically, however, the FL direction is from an Access Network station to an Access Terminal station.
RL transmission of information strictly in support of FL data transfers, such as acknowledgment and DRC information, constitutes signaling “overhead.” It is desirable to minimize the proportion of bandwidth and power that must be allocated for such overhead, while increasing the amount of FL data that is conveyed. Transmission protocols that are efficient for data communication, as opposed to voice communication, may be called “data only” or simply “DO.”
Where legacy CDMA systems having preexisting channel carriers allocated (typically occupying spectrum with a bandwidth of 1.25 MHz or 5 MHz), it is desired to increase data transmission rates while retaining the preexisting channel carrier allocations. To do so, it is possible to transmit data concurrently through a plurality of different FL channel carriers (of, e.g., 1.25 MHz or 5 MHz each). Such plural-carrier transmissions are referred to as “multicarrier” transmissions for data only, or MC-DO. As data rates continue to increase, even WCDMA, which has a carrier bandwidth of 5 MHz, will benefit from multicarrier operation.
In order to maximize system capacity, there is a need to select an architecture and protocol that will permit asymmetric MC-DO transmissions to be as efficient as possible. Existing proposals do not gracefully enable a single RL feedback carrier to convey acknowledgment and DRC information for a multiplicity of FL carriers. The method and system set forth herein address the need for efficient and expandable operation at continuously increasing data rates, while retaining compatibility with legacy systems, and thus resolve the problems noted above.